Droughts are weather extremities that are so hostile that numerous sci-fi and post-apocalyptic stories use them for doomsday scenery, and it’s no wonder. Drought is part of the reality-based scenario of current climate change, as mixed drifts in rainfall and evaporation are creating more dry conditions in some areas. However, understanding this is a dare as more rain seems to fall on other regions, drought settings are naturally changing, and historical rainfall data comes with limitations.
A new study conducted by NASA’s Kate Marvel gathers all these local drought atlases together with recent information and climate model simulations to see what they can disclose about human impact on drought ever since year 1900.
A global atlas
The scientists’ concept was alike other studies that have investigated patterns of climate change for a human mark. Lots of climate-model simulations were mixed together to pinpoint the anticipated long-term drought trend led by human-induced climate change. Real-world data was then studied to see if a similar pattern has occurred from the regular range of natural variability.
This kind of analysis breaks things down to a signal-to-noise ratio which means that the stronger the human-caused signal sticks out from the natural, noisy fluidity, the more evident it is that humans are changing the climate. When the alterations are strong enough, the pattern leaves the range of past occurrences totally and enters what is in fact an uncharted area.
The model simulations with human greenhouse gas diffusion show the vast patterns seen in the study, which turns toward more drought in North America and Europe but rising wet climate around India and western China. The way this happens over the 20th century is curious, leading the scientists to put brackets on three periods: 1900 to 1949, 1950 to 1975, and 1982 to the present time.
The three trends
The signal of human-induced patterns in drought became extremely clear over the first half of the century. The signals were crossing the 90% statistical confidence rank, but then, through the 1950s, 1060s, and 1970s, the worldwide temperature socked, mainly because of rapid growth in sunlight-reflecting aerosol pollution. This took back the signal to the noise level.
However, defining this as aerosol-driven is complicated for aerosol pollution affects rain in intricate ways that are different from greenhouse gas-induced warming, and these interplays are still not a strong point for climate-model simulations. The last period begins in 1982 when a few newer drought data sets appeared online. The data again turns toward the greenhouse gas-caused signal, but they don’t entirely leave the level of natural fluctuations.
Because the model simulations continue in the future utilizing a story of high greenhouse gas emissions, the researchers also checked to see where these patterns are going to. This means that we can anticipate the human signal to be heard clearly from the noise in the close future. The worldwide signal passes the 99% statistical confidence level by the mid-2030s, even if most individual areas take longer. Europe and regions of Asia would emerge by the 2040s, and North America and Mexico come after in the 2060s.
The idea of this study is that numerous observational data sets and reconstructions confirm that human actions were most likely affecting the global risk of droughts as early as the 20th century. The researchers warn that the human consequences of this warming are going to be extreme, especially in North America and Eurasia.
Emmy Skylar started working for Debate Report in 2017. Emmy grew up in a small town in northern Manitoba. But moved to Ontario for university. Before joining Debate Report, Emmy briefly worked as a freelance journalist for CBC News. She covers politics and the economy.